In a radio communication system which links multiple subscribers to a central communications node, there is a need to make use of high gain antenna beams in order to connect these subscribers with the central communications node. For substantially wideband multi-user communication systems, the use of high gain antenna beams is necessary in order to provide a positive link margin between the communications node and the plurality of subscribers. This is especially true in a wideband communication satellite system where multiple earth-based subscribers are linked to a communications satellite network through wideband data links. In such a system, very large antennas are required at the communication satellite in order to provide a positive link margin between each earth-based subscriber and the communication satellite.
In a communication satellite, a phased array antenna can be used to create high gain transmit or receive beams. Typically, as more surface area is provided by the phased array antenna, the gain of the transmit or receive antenna beam increases. In a satellite system which requires multiple satellites in orbit about the earth, the use of very large antenna arrays arranged as a rigid structure can be cost prohibitive. Therefore, when large antenna arrays are to be deployed in space, it becomes advantageous to assemble the array in space on a section-by-section basis. The most desirable method of sectionally constructing a large space-based phased array antenna is to launch the satellite with the antenna folded within the payload volume of the launch vehicle and allow the antenna to unfold after deployment of the satellite.
When a multi-sectioned phased array antenna is unfolded, misalignments between adjacent sections can occur. These misalignments cause the portions of the beam generated by each individual section of the array to be less than optimally combined in front of the antenna. The misalignments cause errors which degrade the performance of the communication system in that they reduce the gain of the transmit or receive antenna beam generated by the satellite. If, however, the error in the pointing angle can be discerned, the beam coefficients for the particular misaligned section can be adjusted to enable the antenna beam to point in the correct direction.
Errors in the pointing accuracy of receive or transmit antenna beams can also be caused by the loss of elements which comprise the phased array antenna section. In a receive antenna, the loss of elements can be caused by the failure of receive electronics, such as low noise amplifiers, which are coupled to each antenna element. In a transmit antenna, the loss of elements can be caused by the failure of solid state power amplifiers which are coupled to each transmit antenna element.
Therefore, what is needed are a method and system for remote calibration of sectionally assembled phased array antennas. Such a system would enable the rapid correction of beam pointing errors caused by any misalignment in the unfolded antenna array, or the loss of antenna elements which comprise a particular phased array antenna section.